Various vehicles include an anti-lock braking system (ABS)/traction control/vehicle stability control module, or an ABS/hydraulic control unit (HCU). Most, if not all, ABS/HCUs have multiple isolation cartridges that are operatively connected to the wheels. For example, a standard automobile includes four isolation cartridges, with each isolation cartridge operatively connected to a respective wheel.
Each isolation cartridge allows brake fluid from a master cylinder to pass to the brakes during normal vehicle operation. During normal operation, the cartridge is open. However, during an ABS event, the cartridge closes to isolate the master cylinder from the brakes. The closing of the cartridge prevents the wheel from locking.
FIG. 1 illustrates an axial cross-sectional view of a check filter assembly 10. The assembly 10 is typically contained within an isolation cartridge. During operation, brake fluid first passes through an inlet filter 12. The inlet filter 12 is configured to prevent contaminants from clogging a critical orifice and sealing surface of the assembly 10. The fluid then passes through a center orifice 14 of the assembly 10. At the same time, the inlet fluid also forces a check ball 16 against an angular sealing surface 18 that defines a portion of a bore 19.
In general, the sealing surface 18 needs to be robust enough to prevent any brake fluid from leaking past the check ball 16 when the fluid pressure forces the check ball 16 against the sealing surface 18.
As shown in FIG. 1, a tappet is positioned in a tappet bore 20. The tappet is generally a plastic cylindrical rod that closes above the center orifice 14. When the tappet closes, the brake fluid pressure is high. The inlet side of the assembly may need to withstand pressure around 350 bars (5075 psi) when the tappet is in the closed position. The pressure forces the check ball 16 against the angled sealing surface 18.
However, it has been found that manufacturing an assembly having an acceptable sealing surface on all parts is difficult. Typically, the sealing material is composed of a material that is capable of withstanding brake fluid pressure applied to the inside walls of the assembly. However, when a part is being molded, it is difficult to control how carbon or glass fibers of the material orient themselves. Therefore, the fibers can potentially orient themselves in such a way that creates a leak path on certain parts, while not causing a leak path on other parts.